EXPERIMENTAL INVESTIGATION OF OXYFUEL COMBUSTION OF RDF AND WOOD CHIPS IN A GRATE INCINERATION SYSTEM

Abstract

Combustion experiments of dried wood chips and refuse derived fuel (RDF) under air and oxyfuel conditions have been performed in an extendedly modified 240 kW_Th pilot-scale grate incineration facility with forward acting grate. To get insight into differences of the combustion processes between air and oxyfuel operation the concentrations of the main flue-gas species have been measured at the end of the combustion chamber and throughout the furnace. Additionally, the temperature has been measured inside the grate bars and the fuel bed as well as along the flue-gas pathway. It could be demonstrated that oxyfuel combustion of wood chips leads to stable CO₂ concentrations in the dry flue gas above 80 vol. %. During oxyfuel combustion of RDF similar trends have been observed; however, the combustion has shown significant fluctuations due to fuel-feeding issues. Profile measurements revealed a spatially extended reaction zone in the oxyfuel cases compared to the respective air combustion cases but with decreasing differences towards the end of the combustion zone. Wet flue-gas recycling has been applied to the experimental system which led to significantly higher H₂O concentrations in the furnace during oxyfuel operation. Concentrations of CO, NO, SO₂, and HCl in the flue gas have been increased during oxyfuel combustion. Especially during RDF oxyfuel combustion the concentration of HCl and SO₂ in the flue gas has been very high. In such a case it would be necessary to recycle the flue gas after appropriate cleaning steps. Also, considering the significantly lower flue-gas volume flow towards the atmosphere absolute emissions seem to be manageable.